1. Field of the Invention
The present invention relates to a blind rivet fastener.
2. Description of Related Art
Rivets are commonly used to fasten together two workpieces. Conventional solid rivets are pressed into corresponding holes of the workpieces by placing an anvil on one end of the rivet and pressing the opposite end of the rivet with a hammer. The installation of solid rivets requires access to both sides of the combined workpieces.
There does exist assemblies that do not allow access to both sides of the combined workpieces. For example, the inner chamber of an aircraft fuel tank is not accessible when the tank is being sealed. To properly seal the tank, there has been developed "blind" rivet fasteners which can be installed from only one side of the workpieces.
A typical blind rivet fastener assembly has a sleeve that is inserted into matching holes of the workpieces. The sleeve has a head on the accessible side of the workpieces. Extending through the inner channel of the sleeve is a stem. The stem contains a head, a shoulder and a serrated pull portion. The stem head is located on the inaccessible side of the workpieces.
The fastener is installed by holding the sleeve while pulling the serrated portion and stem shoulder through the inner sleeve channel. The stem head typically has a tapered shoulder or a separate collar that bends the end of the sleeve in a radially outward direction. The deformed sleeve forms a bulb on the inaccessible blind side of the workpieces. The bulb and the sleeve head fasten the sleeve to the workpieces. The fastener assembly may further have a locking ring which bends and secures the stem to the sleeve. The rivet stem is pulled until the locking features prevent further movement of the stem and the serrated pull portion breaks away from the shoulder.
U.S. Pat. No. 5,052,870 issued Pratt et al. and assigned to Textron, Inc., discloses a blind rivet fastener which has a shear ring that is adjacent to the blind end of the sleeve. When the stem is pulled through the sleeve channel, the shear ring deforms the sleeve to create a bulb. The shear ring and sleeve typically have matching tapered surfaces that induce the outward deformation of the sleeve.
The shear ring of the Textron fastener has an inner annular flange that is located within an outer annular groove of the stem. The inner annular flange shears from the ring to limit the amount of clamping compression of the workpieces. The inner diameter of the shear ring annular flange is smaller than the outer diameter of the stem shoulder. For this reason, the Textron product is assembled by bending the shear ring around the circumference of the stem. The bending process increases the cost of producing the assembly. It would be desirable to provide a blind rivet fastener which has a bulb forming collar that does not have to be bent around the stem to assemble the fastener.